1. Field of the Invention
This invention relates in general to water heating systems and in particular to such systems which utilize solar energy.
2. Description of the Prior Art
Solar energy devices which utilize the sun's radiant energy for heating some medium are well known in the art. Such devices may include an air-to-air heat transfer mode or air-to-liquid. Conventional solar energy collectors are often designed with a box-like enclosure covered with a glass pane or lens and having some type of flow conduit therethrough. As radiant energy strikes the surface of the glass pane or lens, a majority of the heat energy will be absorbed within and a minimum amount of heat energy will be reflected off and lost. As heat energy is absorbed within the box-like enclosure, the temperature of the medium flowing through the conduit will be elevated. This medium, very often water, is then transferred to a use location and/or placed in a storage container for use at a later time when there may not be sufficient sunlight to satisfy the heating demands. Of course, a conventional water storage container is a hot water heater which is normally thought of supplying hot water in response to electric or natural gas heating units. However, it is possible to supplement these electric or gas heating elements with solar energy thereby reducing the demand on the limited and more expensive forms of energy. One such system has been offered by State Industries, Inc. of Ashland City, Tennessee. This system is detailed in a "Solarcraft" brochure and utilizes an energy-absorbing fluid which circulates between the solar panel and a heat exchanger jacket which surrounds the water storage tank. A similar system has been offered by American Heliothermal Corporation of Denver, Colorado. This system which is detailed in a publication entitled "Residential Domestic Hot Water System," also incorporates an annular jacket positioned about the water tank and utilizes an energy-absorbing fluid to supplement the heating of the water within the tank.
Both of these systems involve a heat exchanger having a single passageway and a single fluid therein. The entire extent of the heat transfer to the water within the tank, which will ultimately be used at a remote location, is from the energy-absorbing fluid through the heat exchanger surface and then through the wall of the water storage tank. In order to heat all of the water within the tank, heat must be applied to the exterior of the tank for sufficient length of time in order to allow heat to transfer through the tank wall and then through the outer portions of water to reach the inner portions of water. Of course, with any solar energy system, the object is to retain and efficiently utilize as much of the radiant energy as possible. One way to do so, is to reduce thermal insulation between the energy absorbing fluid and the water so that unproductive heat dissipation is held to a minimum level.